1. Field of the Invention
The present disclosure relates to a method and an apparatus for transmitting and receiving Downlink Control Information (DCI) in case of supporting 256-state Quadrature Amplitude Modulation (256QAM). More particularly, the present disclosure relates to a method and an apparatus for transmitting and receiving DCI including a Modulation and Coding Scheme (MCS) index for supporting 256QAM in addition to typically used three modulation methods, such as Quadrature Phase Shift Keying (QPSK), 16-state Quadrature Amplitude Modulation (16QAM) and 64-state Quadrature Amplitude Modulation (64QAM).
2. Description of the Prior Art
Information may be transmitted through a signal using signal properties such as intensities, displacements, frequencies, and phases thereof. Modulation is a process of transforming such signal properties into proper waveforms according to a channel characteristic of a transmission medium. Also, a digital signal may be used to transmit digital information by mapping the digital information to one of bit stream and a digitalized analog signal (sampled or analog-to-digital converted signal). Digital modulation is a process of transforming such digital signal (e.g., digital symbol sequences) to a proper signal according to the channel characteristics of a transmission medium. As a representative digital modulation method having good bandwidth efficiency, an M-ary QAM modulation method is used. The M-ary QAM modulation method may be expressed as 2M QAM and the M-ary QAM modulation method includes QPSK (or 4QAM), 16QAM and 64QAM.
Various modulation methods are used for downlink (DL) data transmission in a wireless communication system such as Long Term Evolution (LTE) or LTE-Advanced. Such modulation methods include QPSK, 16QAM and 64QAM. By using these modulation methods, a Base Station (BS) transmits data to a User Equipment (UE), and the UE demodulates the transmitted signal and receives the data.
Recently, an amount of data transmitted and received between terminals and associated base stations has been increased abruptly due to sharp increase in the number of user terminals and in the data usage. This requires a modulation method that can rapidly process a large amount of data traffic.
Meanwhile, a BS selects one of the modulation methods based on a DL channel status, and notifies the UE of the selected modulation method by using DCI. The UE may identify the selected modulation method based on the received DCI and may receive the data through demodulation appropriate for the data modulation method.
To this end, the UE measures the DL channel state, and transmits information on the measured DL channel state to the BS. Also, the BS includes, in the DCI, predetermined parts of MCS index information respectively mapped to QPSK, 16QAM and 64QAM, and transmits the DCI including the predetermined parts of MCS index information to the UE. However, due to sharp increases in data traffic and data speed, a new modulation method has been demanded. Furthermore, it has been also demanded for a method for indicating such a new modulation method in the DCI having a limited size.